It probably seemed like a good idea at the time. Southern Railway this morning asked passengers facing 14 more days of strikes to describe how industrial action makes them feel.

But the train operator's attempt to gain Twitter users' support during the long-running trade union dispute appeared to have backfired when it sparked a backlash from commuters.

At the height of the Monday morning rush-hour, it used the social network to ask followers to send messages to the Rail, Maritime and Transport union (RMT) to "tell them how rail strikes make you feel".

But the tweet, with an image headlined "Let's Strike Back", prompted an angry response from dozens of customers - who face five more blocks of strike action from next month.

Meanwhile, Southern has set a deadline of Thursday for the RMT to accept an offer aimed at averting strikes.

Otherwise, the company has said it will terminate conductors' contracts and press ahead with changes to their role.

Mick Cash, leader of the Rail, Maritime and Transport union, said: "This is a pathetic attempt by the basket case Southern franchise to once again try and blame their frontline staff for their own managerial incompetence.

Southern have wrecked services across the South East and the passengers know thatMick Cash, RMT

"Southern have wrecked services across the South East and the passengers know that and that is why the commuters themselves are mounting a legal challenge against the company.

"RMT thanks the public for their continued support and understanding as we continue to fight for services and safety against this money-grabbing outfit."

Southern said its new offer included a lump sum payment of £2,000 to conductors to be paid once the dispute is settled and its plans are fully implemented.

Its eight-point offer includes guarantees on conductors' jobs until 2021, above-inflation pay increases for the next two years and guaranteed levels of overtime.

In a letter to RMT leader Mick Cash, Southern said it will "regretfully proceed without the RMT's involvement" and serve notice letters to conductors, terminating their contracts and inviting them to sign up to the new on board supervisor role from January if it does not agree to the offer by midday on Thursday.

A Southern spokesman said: "Our aim was to get the debate going and to let people know exactly what our very fair and comprehensive offer is and how we are trying to modernise the train service for our passengers which the RMT leadership is trying to block.

"Our service has not been good enough and the main reason for that has been the RMT union leadership's refusal to talk and do a deal. Thousands of passengers are demanding to know what we are doing to bring this dispute to an end. We felt there was a need to let them know.

"Today we have reaffirmed that offer in a final attempt to bring this to an end and we are offering an additional incentive of £2,000 once the new role is introduced. Faced with a further 14 days of strikes, we believe enough is enough - the union leadership has had this offer for two months and should put it to their members."